Four Los Alamos National Laboratory (search) workers were fired and one will resign under pressure for their roles in a security and safety scandal at the lab, the lab's director said Wednesday.

The fired workers were among 23 suspended this summer after two computer disks containing classified information went missing and an intern was injured in a laser accident. The discovery of the missing disks July 7 prompted a virtual shutdown of the nuclear lab, idling roughly 12,000 workers.

A lab official originally said five workers were terminated, but a spokesman later clarified that by saying four employees were terminated and one "will resign in lieu of termination."

Of the remaining 18 employees, seven were subject to other discipline such as demotion from management, salary reductions or written reprimands. One remains on investigatory leave. Ten will return to their positions with a finding of "no wrongdoing."

"It's very important to get this behind us," Director Pete Nanos said in a phone interview with The Associated Press. Nanos spoke by cell phone from an airplane after meetings in Washington, D.C.

Nanos declined to discuss specific cases of fired employees but said that some were dismissed for "not taking actions that you were supposed to take, or signing off on things that you hadn't done." Another employee had not taken appropriate precautions in a safety area.

"We really did fit the punishment to the acts that were done," Nanos said.

Three of the workers will leave the lab in connection with the missing computer disks; the other two were involved in an accident in which a laser injured an intern, he said.

"These personnel actions touched all levels of employment, staff and management and varying levels of tenure," lab spokesman James Fallin said. He declined to be more specific about the lab departments or positions involved.

Nanos also said the northern New Mexico (search) lab has finished its investigation into the two missing disks, also known as "classified removable electronic media," or CREM. Information from the probe has been turned over to federal authorities. Nanos refused to release additional details. He said other agencies are still investigating.

Nanos, who held a series of all-hands meetings with lab workers after the scandal broke, added that the "commitment of employees right now is extremely high."

Fallin emphasized "that today's announcements provide very clear evidence that it's not business as usual at this laboratory. ... Accountability is the order of the day."

The University of California operates the lab under a contract with the Energy Department (search). S. Robert Foley, the university's vice president for laboratory management, said the disciplinary action was important.

"This action moves [the lab] one step closer to completing the restart of all activities," he said.

Problems at Los Alamos have drawn criticism from Congress and senior officials at the Energy Department, putting in question the fate of the 61-year-old institution -- the birthplace of the atomic bomb. The Los Alamos management contract has been put up for bid for the first time in the lab's history.